Power line communication (PLC) systems are contaminated with complicated noise. Five types of noise in power line communication systems are introduced in this paper. According to their properties, these noises are mainly divided into two types that are background noise and impulsive noise. Noise modelling approaches for background noise and impulsive noise are reviewed in this paper. A frequency-domain based model is applied to describe the properties of background noise and a frequency decreasing power spectral density (PSD) is revealed based on this model. The values of PSD are between-140dBm/Hz and-80dBm/Hz. A time-domain approach which is based on partitioned Markov chain is applied to describe the time behaviour of impulsive noise. Simulation results showed this model is suitable for the description and modelling of impulsive noise. This model revealed that impulsive noise rarely exceeds a few milliseconds.